Blooms of diatoms in the genus Pseudo-nitschia, which produce a neurotoxin called domoic acid, are a regular occurrence in coastal waters. During large blooms, the algal toxin enters the food chain, forcing the closure of some fisheries (such as shellfish and sardines) and poisoning marine mammals and birds that feed on contaminated fish. But until now, blooms of these algae in the open ocean have attracted little attention from researchers.

Study lead author, Mary Silver says that normally pseudo-nitschia don't have much effect, but "these species are incredibly responsive to iron, often becoming dominant in algal blooms that result from iron fertilization. Any iron input might cause a bloom of the cells that make the toxin." Silver adds that natural deposits of iron in the open ocean (from volcanic eruptions, dust storms, etc) have occurred for millions of years, but are sporadic occurrences.

"To do iron enrichment on a large scale could be dangerous," Silver notes, "because, if it causes blooms of pseudo-nitschia, the toxin will get into the food chain, as it does in the coastal zone."

Old Samples From Iron Fertilization Experiments Showed ToxinsHow did Silver and colleagues reach this conclusion (and warning)? By examining pseudo-nitschia cells found in samples collected from the Gulf of Alaska in 2007, which ended up showing the presence of domoic acid. This prompted a reexamination of old samples from ocean iron fertilization experiments from 1995 and 2002--which, despite the age of the samples and the assumption that is would have broken down, still contained the toxin.

Breaking an Ecosystem Easier Than Fixing OneObviously the efficacy of any particular geoengineering method can't be determined by one study--and there a examples both proving both its worth or lack thereof, as well as ones like this showing potential unintended consequences--and more research would be needed to determine that. But since, as Coale aptly puts it, "It is much easier to break an ecosystem than it is to fix one," the scale at which such research is conducted, so as to minimize potential side effects to the wider ecosystem, is not a trivial concern.